We use a 30‐year time series (1986–2016) of dichlorodifluoromethane (CFC‐12) concentrations with a refined transit time distribution (TTD) method, to estimate the temporal variation of anthropogenic carbon (C_ant) in the Central Labrador Sea. We determined that the saturation of CFC‐12 and sulfur hexafluroide (SF₆) in newly‐formed Labrador Sea Water had departed significantly from 100% and varied systematically with time. Multiple linear regression of the time‐varying saturation, with the tracer's atmospheric growth rate and the wintertime mixed layer depth as independent variables, allowed reconstruction of the saturation history of CFC‐12 and SF₆ in wintertime surface waters, which was implemented in the TTD method. Use of the time‐varying saturation for CFC‐12 gave C_ant concentrations ∼7 μmol kg⁻¹ larger than estimates obtained assuming a constant saturation of 100%. The resulting C_ant column inventories were ∼20% larger and displayed lower interannual variability compared to conventional TTD‐based estimates. The column inventory of C_ant increased at an average rate of 1.8 mol m⁻² y⁻¹ over the 30‐year period. However, the accumulation rate of C_ant was higher than this average in the early 1990s and since 2013, whereas inventories remained almost unchanged between 2003 and 2012. The variation in the C_ant accumulation rate is shown to be linked to temporal variability in the relative layer thickness of the annually ventilated Labrador Sea Water and the underlying Deep Intermediate Water. The non‐steady C_ant accumulation highlights the importance of sampling frequency, especially in regions of variable deep mixing and high carbon inventories, and potential misinterpretation of C_ant dynamics.

中文翻译：

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基于瞬态示踪剂的30年时间序列，基于中拉布拉多海的人为碳估计

我们使用30年时间序列（1986-2016）的二氯二氟甲烷（CFC-12）浓度和改进的渡越时间分布（TTD）方法来估算拉布拉多海中部人为碳（C _ant）的时间变化。我们确定，新形成的拉布拉多海水中的CFC-12和六氟化硫（SF ₆）的饱和度与100％显着偏离，并且随时间而系统地变化。随时间变化的饱和度的多元线性回归，以示踪剂的大气增长率和冬季混合层深度为自变量，可以重建CFC-12和SF ₆的饱和度历史在TTD方法中实施的冬季地表水。对于CFC-12使用随时间变化的饱和度，其C _ant浓度比假设恒定饱和度为100％时获得的估计值大约7μmolkg ^-1。与传统的基于TTD的估计相比，所得的_Cant列库存增加了约20％，并且显示出较低的年际变化。在过去的30年中，C _ant的色谱柱库存量平均以1.8 mol m ^-2  y ^-1的速度增加。但是，C _ant的累积率高于1990年代初和2013年以来的平均水平，而2003年至2012年之间的库存几乎保持不变_。Cant积累率的变化与每年通风的拉布拉多海的相对层厚度的时间变化有关。水和潜在的深层中间水。不稳定的C _ant积累突显了采样频率的重要性，尤其是在可变深度混合和高碳存量的地区，以及对C _ant动态的潜在误解。